The invention pertains to the field of reflective displays and methods of manufacture. More particularly, the invention pertains to addressing electrophoretic, electrochromic, and bi-chromal sphere displays and fabricating such displays using fibers.
There are several different methods of producing a reflective display. The most well known and widely used method is to use liquid crystal molecules as the electro-optic material. In the liquid crystal family, a vast range of molecules could potentially be used to create reflective displays. Some of these liquid crystal molecules include, twisted nematic, cholesteric-nematic, dichroic dye (or guest-host), dynamic scattering mode, and polymer dispersed to name a few. Most of these liquid crystal molecules require other films, such as, alignment layers, polarizers, and reflective films.
Another type of reflective display composing an electro-optic material is an electrophoretic display. Early work such as that described in U.S. Pat. No. 3,767,392, xe2x80x9cElectrophoretic Light Image Reproduction Processxe2x80x9d, used a suspension of small charged particles in a liquid solution. The suspension is sandwiched between to glass plates with electrodes on the glass plates. If the particle have the same density as the liquid solution then they will not be effected by gravity, therefore the only way move the particles is using an electric field. By applying a potential 7 to the electrodes 5, the charged particles are forced to move in the suspension to one of the contacts. The opposite charge moves the particles to the other contact. Once the particles are moved to one of the contact they reside at that point until they are moved by another electric field, therefore the particles are bistable. The electrophoretic suspension is designed such that the particles are a different color than the liquid solution. Therefore, moving the particles from one surface to the other will change the color of the display. One potential problem of this display is the agglomeration of the small charged particles when the display is erased, i.e., as the pixel is erased the particles are removed from the contact in groups rather than individually. The invention of microencapsulating the electrophoretic suspension in small spheres solves this problem, U.S. Pat. No. 5,961,804, xe2x80x9cMicroencapsulated Electrophoretic Display.xe2x80x9d FIG. 1 shows the typical operation of a microencapsulated electrophoretic display. In this display the particles are positively charge and are attracted to the negative terminal of the display. The charged particles are white and the liquid solution they are suspended in is dark, therefore contrast in the display is optionally achieved by selectively moving some of the particles form one contact 5 to the other 5. In this type of display, the electro-optic material is the electrophoretic material and any casing used to contain the electrophoretic material.
A similar type of electro-optic display, a twisting ball display or Gyricon display, was invented by N. Sheridon at Xerox, U.S. Pat. No. 4,126,854, xe2x80x9cTwisting Ball Display.xe2x80x9d It was initially called a twisting ball display because it is composed of small spheres, one side coated black, the other white, sandwiched between to electroded 5 glass plates. Upon applying an electric field 7 the spheres with a positive charged white half and relative negative charged black half are optionally addressed (rotated). Once the particles are rotated they stay in that position until an opposite field is applied. This bistable operation requires no electrical power to maintain an image. A follow on patent, U.S. Pat. No. 5,739,801, disclosed a multithreshold addressable twisting ball display. In this type of display, the electro-optic material is the bichromal spheres and any medium they may reside in to lower their friction in order to rotate.
The last major electro-optic display is that produced using an electrochromic material. An electrochromic display, similar to that in U.S. Pat. No. 3,521,941, xe2x80x9cElectro-optical Device Having Variable Optical Densityxe2x80x9d, is a battery which has one of the electrodes serving a display function. An electrochemical display stores electrical energy by changing it into chemical energy via an electrochemical reaction at both electrodes. In this reaction, electrochemically active material is plated-out on one of the contacts changing it from transparent to absorbing. FIG. 3 shows the typical reaction of an electrochromic display, where an electrochemical reaction from the applied voltage causes material to plate out on the negative terminal of the display. In this type of display, the electro-optic material is the electrochromic material, which is sandwiched between the electroded plates.
Most of the electro-optic displays have problems with addressing the display. Since most of the electro-optic materials do not have a voltage threshold, displays fabricated with the materials have to be individually addressed. Some of the liquid crystal materials use an active transistor back plane to address the displays, but these type of displays are presently limited in size due to the complicated manufacturing process. Transmissive displays using liquid crystal materials and a plasma addressed back plane have been demonstrated, U.S. Pat. No. 4,896,149, as shown in FIG. 4, however, a reflective display using such a technique has not be disclosed. In addition, displays fabricated using the plasma addressed back plane shown in FIG. 4 are also limited in size due to availability of the thin microsheet 33. One potential solution for producing large size displays is to use fibers to create the plasma cells as shown in FIG. 5. Using fibers to create a plasma cell was first disclosed in U.S. Pat. No. 3,964,050, and using fibers to create the plasma cell in a transmissive plasma addressed liquid crystal display was disclosed in U.S. Pat. No. 5,984,747.
The invention includes the use of fibers with wire electrodes to construct reflective fiber-based displays, where reflectivity is formed by modulating an electro-optic material within the display. A plasma channel is optionally built into the display to address the electro-optic material. The plasma channel is optionally totally contained within the fibers and addressed using wire electrodes. The wire electrodes are contained within the fiber or on the surface of the fiber. The fibers are optionally colored to impart color to the display, or are optionally black to serve as an absorbing layer to enhance the contrast of the display, or white to enhance the reflectivity of the display. The electro-optic material consists of a liquid crystal material, electrophoretic material, bichromal sphere material, electrochromic material, or any electro-optic material that can serve to create a reflective display. In addition, colored pigment is optionally added to the electro-optic material to impart color to the display. The fibers are optionally composed of glass, glass ceramic, plastic/polymer, metal, or a combination of the above.